Welding system



Nov. 12, 1940. J. w. DAWSON WELDING SYSTEM 3 Shets-Sheet 1 Filed Aug.13, 1938 INVENTOR /0/. flL dn/J zz.

WITNESSES:

ATFORNE Nov. 12, 1940. J. w. DAWSON WELDING SYSTEM Filed Aug. 13, 1938 3Sheets-Sheet 2 INVENTOR AA .7 Man o/z ATTORN NOV. 12, 194% 3 w. DAWSON2,221,576

WELDRG SYSTEM Filed Au 13, 1938 3 Sheets-Sheet s WITNESSES: V INVENTORJ34 7:v V

Patented-Nov 12, 1940 PATENT OFFICE WELDING SYSTEM John W. Dawson,Auburndalc, Mass, assignor to Westinghouse Electric 6: ManufacturingCompany, East Pittsburg Pennsylvania 7 11, Pa., a corporation ofApplication August 13, 1938, Serial N0. 224,709

Claims.

My invention relates to a welding system and especially a welding systememploying long leads carrying heavy currents.

An object of my invention is to utilize a con- 5 tact rectifier insupplying the welding current directly to the welding electrodes.

Another object of my invention is to improve the power factor and lowerthe kva. rating of the transformer supplying current to weldingelectrodes having long leads.

A further object of my invention is to provide a welding system whichshall be capable of drawing power from a polyphase network distributingthe loading uniformly over all of the 5 phases.

A still further object of my invention is to provide a weldingarrangement which, while supsupplied from an alternating source, shallbe capable of delivering direct current for welding.'

Other objects and advantages of my invention will be apparent from thefollowing description and drawings, in which:

Figure 1 is a diagrammatic circuit illustrating a preferred embodimentof my invention;

Fig. 2 is a perspective view of a contact rectifler utilized in thecircuit of Fig. 1;

Fig. 3 is a perspective view of a row of contact rectifier plates in thestructure of Fig. 2; and

80 Fig. 4 is a diagrammatic circuit illustrating a preferred controller,timer and interrupter for the circuit in Fig. 1.

Certain types of welders necessarily employ long leads, and these leadscarry heavy currents. This is especially true ofthe gun" type portablespot welders. These long leads from the secondary of the transformercarry heavy currents and the power factor is very poor, and the kva.rating of the transformer is correspondingly high. I have devised ascheme whereby apparatus is utilized employing low voltage and highcurrent in the secondary of the welding transformer, so that the weldingleads operate at the frequency of the welding spots instead of at thefrequency of the line commercial voltage. In my preferredembodiment, I-accomplish this result by utilizing a very large rectifier, preferablyof the copp r oxide type, in the secondary circuit of the weldingtransformer to supply rectified current to the welding electrodes. I

It is to be noted, moreover. that for certain welding operations as, forexample. with certain forms of aluminum, direct current is to bepreferred to alternating current.

u In.l"ig. 1.Ihsvedil'clo|edsthrce-piusonip-' ply circuit W, H and i2feeding into a controller timer and interrupter 93, which may be of anysuitable type, and preferably that disclosed in Fig. 4. The three-phasecurrent feeds into the delta transformer primary H to supply energy 0 tothe three-phase star-connected secondary 16. The secondary i5 has itslegs tapped as at ii for adjustment. The transformer M and I5 ispreferably designed to transform alternating current at 60 volts intocurrent at 6 volts. The value W of the current in the secondary israised up to the other of 10,000 or 20,000 or 30,000 amperes, or more.The three legs i1, I8 and it of thesesondary W are connected to a largemulti-plate contact rectifier 20, preferably of the copper or:- 5 ldetype. This copper oxide rectifier is diagram matlcally illustrated inFig. 1 and in perspective in Fig. 2. A detailed view of one of theseries of plates is illustrated in Fig. 3. The three legs l1,

l0 and is make connections to the junctures 2|, 80 Hand 23 between thetwo series of plates. 0n one side, these contacts are to the copperoxide surface 24 of the rectifier plates, whose copper surface 25underneath the oxide makes contact with the positive bus bar 26. Thecontacts 2i, 26 22 and 23 on the other side make contact to the copper21 of a series of plates whose copper oxide 20 is connected to thenegative bus bar 29.

A connection 30 from the positive bus bar and the connection 3! from thenegative bus bar 80 makes contact with the welding electrodes 32 and 33.The welding load 34, to which these electrodes may be applied, is, ofcourse, of any type and especially of a type demanding a heavy currentat low voltage.

In Fig. 2 is illustrated a preferred structure of the copper oxiderectifier. The connections for the three-phase alternating current arerespectively applied to the metal portion of U-shaped copper bars 2i, 22and 23. These copper bars have their parallel legs II and 21 connectedto a series of plates whose preferred arrangement is disclosed in Fig.3. The plates 40 are preferably of the-oblong shape illustrated, coatedwith copper oxide except for the upper portion 4! sur- 6 rounding a holethrough which extends a rod 42, Contact is made to the exposed copperand to the exposed copper of the adjacent plates by conducting washers42 on the rod 42 between the plates. The lateral edges of the copperoxide coated portion of the plates have clamped thereon a U-shaped edgepiece It having an extensive linear contact with the copper oxide. TheseU- shapedstraps extend into an integral loop orextensionllatthcotherendofth'ercctanlularlb plates making a contact to arod 46 having thereon conducting washers 41 making contact to adjacentextensions of the straps 45. A plurality of thick copper tabs extendfrom spaced intervals along the rod 42 and likewise thick copper tabs 49extend from spaced intervals along the rod 46. The copper bus bar 36 inFig. 2 is connected by the tabs 43, as shown, to the copper oxideportion of a line of these copper oxide discs. The other adjacent arm 31of .the bus bar is connected by the tabs 43 to the copper portion of thecopper oxide disc. The lower portion or coil of the first row of platesis connected by the tabs to a bus bar that is connected in turn to thecopper end of the first plates of the other two legs 5| and 52 to form acommon positive bus bar 53 corresponding to the bus bar 26diagrammatically illustrated in Fig. 1. The lower portion of therespective other three groups of plates have bars 54 connected throughrods 46 to the copper oxide portion of the plates and also tointerconnections 56 to a common negative bus bar 51 corresponding to thebus bar 29 in Fig. l. The plates are spaced apart so that they can becooled by forced ventilatlon passed therethrough. The plates are also ofsuch a size as to suitably rectify tens of thousands of amperes such as10,000, 20,000 or 30,000.

In Fig, 4, I have disclosed a preferred timing circuit to substitute atI3 in the diagrammatic circuit of Fig. 1. Various types of timingcircuits might be utilized, but I prefer to utilize the specialadaptation of a circuit described in my Patent No. 2,081,987, issuedJune 1, 1937, for

.Electric control system. In Fig. 4, the multiphase connections II, IIand I2 are illustrated,

as well as the delta primary I4 of Fig. 1.

In order to provide for the flow of alternating current under control toand from the delta devices I35, I35, I31, I33, I33 and I40 illustrated.

' These six discharge devices are associated in pairs transformer I4.

witheachoi the connections II, II and I2. Each pair is inverselyconnected as disclosed. It is necessary for a positive half cycle ofalternating current, for example, to enter one of the connections. passthrough a leg of the primary I4, and return by one of the othermulti-phase connections. The timing circuit illustrated is accordinglydesigned to permit such a wave to enter by multi-phase connection II,for example, pass through the discharge device I39, pass through the legI34, for example, of the primary I4, and then pass through the dischargedevice I40 and I returned by the multi-phase connection I2. The

timing circuit illustrated will permit the accurate starting and lengthof such passage by the timing circuit illustrated. Duplicates of thistiming circuit may be applied at 13 and H to permit accurate timing ofthe passage of current through other combinations of the dischargedevices and phases. The energy for the timing circuit is derived from asource such as the primary I4 in phase with the voltage through the mainsupply This may be done by connecting I0, II', I2 to II, II and I2.Primary I4 supplies energy to secondary I4 which in turn supplies thevarious rectiflers, cathodes and transformers of the timing circuit.I34, I34 and I34" are in phase. secondaries I32 and I33 supply energy totiming circuits 13 and 1 I.

The following is a description of the timing circuit as applied betweenthe multi-phase connections I0 and I2: Each of the valves I39, I40 has,respectively, anodes I4I, I42, mercury pool cathodes I43, and controlelectrodes I45, I46. When current is caused to flow from the anodes HI,I 42 through the control electrodes I45, I46 into the mercury poolcathodes I 43, cathode spots are formed on the latter which will causethe valves I39 and I40 to become conducting when thus ignited, providedthat the proper polarity for which they are adapted to be conducting isapplied thereto. In other words, each of the valves I39, I40 will becomeconducting on the application of the'proper polarity or half cyclethereto provided that the cathode spot is formed in the half cycle forwhich either of them is adapted to become conducting. The valves I39,I40 will remain in the conducting state until the end of the half cycleand will not again become conducting, unless during a succeeding halfcycle of the alternating current, a cathode spot is again formed.

In order to energize the control electrodes I45, I46 for the purpose offorming the cathode spots in the valves I39, I40, control circuits showngenerally at I5I, I52 individual respectively thereto are provided. Thecircuits I5I, I52 comprise electric valves I53, I54, respectively, whichare controlled by means of a phase shifting circuit and valves I55, I56,which are disposed to be controlled by the timer device III employing amagnetic impulsing device II8. which is more particularly described inmy Patent No. 2,081,987 referred to above.

The disk III is revolved at one revolution per second by the synchronousmotor H3. The disk III has 120 holes in its peripheral region for usewith cycle alternating current so each hole corresponds to a half cycle.For the half cycles it is desired that the devices shall pass current tothe primary I4, pins II5 are inserted in the holes. A composite core ofpermanent magnets II9 has laminations I23a. and l23b surrounded bycontrol windings I20a, I20b, I2Ia and I2Ib to control the tubes I55 andI55 as disclosed. If four pins are placed in consecutive openings, fourincreases and decreases of magnetic flux across the gap will occur withfour consecutive impulses applied to valves I 55 and I56 to conductcurrent for four half cycles. Where there are no pins in the holes therewill be no impulses and no discharge through I55 and I55.

The valves I53, I54, I55, I56 are preferably of the gas-filled arcdischarge type, and, as illustrated, they are, respectively, providedwith anodes I51, I53, I59, -I50, control electrodes or grids I6I, I62,I63, I64, and hot cathodes I65, I63, I61, I66. A capacitor I69 isconnected between each of the control electrodes I6I, I62, I63, I54 andits respective cathode I65, I65, I61, I63, in

order to maintain the former at a predetermined potential relative tothe latter.

The valves I53, I54 are arranged to control the particular instant ineach half cycle at which the valves I39, I40 are to be renderedconducting. Each of the valves I53, I54 has an individual transformerI1I, I12, the secondary windings I13, I14 of which are connected,respectively, between the control electrode I6I and the cathode I andthe control electrode I62 and the cathode I66. The transformers I1I, I12are provided, respectively, with primary windings I15, I16 which areconnected into a common control circuit I11 having a common terminal I18and a voltage divider I19 provided with a variable tap I80. The voltagedivider I19 and the variable tap I80 therealong is provided in order tocontrol the relative time in each half cycle at which the valves I55,

III are rendered conducting. Due to slight variations in manufacture,the valves I 58, I58 and the associated valves may not have identicaloperating characteristics. In order, therefore, to provide for making acompensation for different operating characteristics of the valves I58,I58, the voltage divider I 19 may be adjusted by moving the variable tapI88 to the desired position.

The time in each half cycle at which the valves I88, I88 are renderedoperative depends upon the phase relationship of the voltage which isimpressed between the common terminal I18 and the variable tap I88relative to the voltage in the legs I88, I88 and I88 of transformers I8,I4, which leg voltages are in phase. This relative phase relationshipmay be altered in order to vary the amount of energy which is suppliedto the load device or the heat supplied to perform a welding operation,by rendering the valves I88, I88 conducting either earlier or later intheir individual half cycles to correspondingly increase or decrease theamount of energy which is sup- .plied to the ioad device. The desiredphase relatlonship of the control voltage for the valves I88, I88 may beobtained from a phase shifting circuit, shown generally at I8 I. Thephase shifting circuit III is energized by means of a transformer, showngenerally at I82, having a primary' winding I88 connected to transformerI8, and a secondary winding I88 having a tap I88 which may be locatedmidway between the ter-v minals thereof. A voltage divider I88 isprovided comprising sections I88a, I88b, and having a variable tap I81movable therealong. An inductor I88 is provided and connected in shuntcircuit relation with the section I88b. It will be observed that twoimpedances are provided by this impedance network. That is, theimpedance represented by the section I88a of the voltage divider I88 andthe impedance having a different phase angle represented by the section"811 of the voltage divider I88 and the inductor I88 connected in shuntcircuit relation therewith.

It will also be observed that I88 of the voltage divider I18 isconnected to the tap I88 of the secondary winding I88 and that thecommon terminal I18 is connected to the variable tap I81. By adjustingthe position of the variable tap I81 along the voltage divider I88, itis possible to vary the phase relation of the voltage applied between.the common terminal I18 and the variable tap I88 of the common controlcircuit I11 as may be desired.

' Thecontrol voltage of substantially constant magnitude is obtained byconnecting the common control circuit I11 between a point of the tap I88and the variable tap I81. In this manner, it is possible to provide asubstantial constant value of control voltage over the entire portion ofeach half cycle during which it may be desirable to render the valvesI88, I88 conducting.

The timer I I8 is provided to determine the particular half cyclesduring which the valves I88,

I88 will be rendered conducting. It will be observed thatthe controlwindings I2Ia, I2Ib of the magnetic impulsing device II8 are connectedIn series circuit relation and to the control electrode I88 of the valveI88, and that the windings II8a, I28b of this device are also connectedin series circuit relation and .to the control electrode I88. Normally,a negative biasing potentisl is applied to the electrode I88, i8 bymeans of rectifiers I8I, I82, respectively. The rectifiers the variabletap I II, I82 may be connected for energization, 'respectively, tosecondary windings I 88, I84 of a transformer, shown generally at I 85,having a primary winding I86 which may be connected to the secondary oftransformer I8. 2

The adJustment of this circuit will determine the number of cycles ofalternating current that will pass from multi-phase connection It tomulti-phase. connection I2 through the primary I8.

I have accordingly devised a system for utilizing very low voltage andhigh current. energy in the secondary of the welding transformer. It isapparent that many modifications may be made in the preferred embodimentillustrated. In particular, it is to be noted that my invention may beapplied where the source is of the singlephase type or has any number ofphases other than three as actually shown. Accordingly, I desire onlysuch limitations imposed on the following claims as is necessitated bythe prior art.

I claim as my invention:

1. A resistance welding circuit comprising a source of alternatingcurrent, a transformer having its primary connected to said source, atiming mechanism interposed between said source and said transformerautomatically controlling the number of cycles of alternating currentapplied to said transformer at a time, a contact rectifier connected inthe secondary of said transformer and welding electrodes connected tosaid contact rectifier.

2. A resistance welding circuit comprising a source of alternatingcurrent, a transformer having its primary connected to said source, atiming mechanism interposed between said source and said transformerautomatically controlling the number of cycles of alternating currentapplied to said transformer, a contact rectifier being connected to thesecondary of said transformer, said contact rectifier comprising aplurality of copper oxide coated copper plates and welding electrodesconnected to said contact rectifier.

3. A welding circuit comprising welding electrodes, connections thereto,a contact rectifier and means for connecting a source of alternatingcurrent to said contact rectifier and for connecting said rectifier tosaid connections to supply output current from said rectifier thereto.the voltage in said connections to the welding electrodes being of theorder of 2 to volts and the current being of the order of ten thomandam- .peres in operation.

4. A resistance welding circuit compriang welding electrodes adapted tobe placed in contact with a welding load, multi-phase connections forsupplying multi-phase alternating current, a rectifier drawing abalanced supply from the various multi-phase connections andsupplyingitsout- .put current to said welding electrodes, and a timingmechanism controlling the number of cycles of alternating currentapplied consecutively to said rectifier.

5. A resistance welding circuit comprising welding electrodes adapted tobe placed in contact with a welding load, multi-p'hase connections forsupplying multi-phase alternating current, a copper oxide rectifierdrawing a balanced supply from the various muiti-phase connections andsupplying its output current to said welding electrodes-and a timingmechanism controlling the number of cycles of alternating currentapplied at a time to said rectifier.

' JOHN W. DAWSON.

